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Endohedral nitrogen fullerenes have been proposed as building blocks for quantum information processing due to their long spin coherence time. However, addressability of the individual electron spin levels in such a multiplet system of 4S3/2 has never been achieved because of the molecular isotropy and transition degeneracy among the Zeeman levels. Herein, by molecular engineering, we lifted the degeneracy by zero-field splitting effects and made the multiple transitions addressable by a liquid-crystal-assisted method.The endohedral nitrogen fullerene derivatives with rigid addends of spiro structure and large aspect ratios of regioselective bis-addition improve the ordering of the spin ensemble. These samples empower endohedral-fullerene-based qudits, in which the transitions between the 4 electron spin levels were respectively addressed and coherently manipulated. The quantum geometric phase manipulation, which has long been proposed for the advantages in error tolerance and gating speed, was implemented in a pure electron spin system using molecules for the first time.

InAs quantum dots (QDs) are grown on planar InP (1 0 0) by metalorganic vapor-phase epitaxy (MOVPE) with a thin GaAs interlayer beneath the QDs. The QDs’ structural and optical properties are investigated when varying the GaAs interlayer thickness, growth temperature, and group V/III ratio and related to As/P exchange, the goal being to obtain high-quality QDs with emission wavelength around 1.55 μm.

Ordered InAs quantum dot (QD) arrays are formed by self-organized anisotropic strain engineering of an InAs/InGaAsP superlattice template on truncated InP pyramids grown by selective-area chemical beam epitaxy. The ordering is changed from one-dimensional on planar substrates to two-dimensional in the limited pyramid top surface areas. Upon shrinking the pyramid top surface area, the photoluminescence linewidth of the QD arrays narrows. This indicates improved size uniformity of the QDs when self-organized in site-controlled, local arrays.

We report the formation of site-controlled InAs quantum dots (QDs) on InP pyramids and their integration into planar structures by metalorganic vapor-phase epitaxy. The QD number is reduced by the shrinking pyramid size during growth. Finally the emission from a single QD is observed at 1.55 µm, after optimization of the growth parameters. Employing regrowth epitaxy, position-controlled InAs QDs are integrated into planar InP structures. A smooth surface morphology is obtained at 640 °C during regrowth.

Number and size control of InAs quantum dots (QDs) on truncated InP pyramids grown by selective area Metal Organic Vapor Phase Epitaxy (MOVPE) is reported. The facet composition of the pyramid top surface and the relative facet sizes are determined by the shape of the pyramid base and the pyramid height for a certain base size. This allows the precise position and distribution control of the QDs due to preferential nucleation on the {103} and {115} facets. The size of the QDs is adjusted by the growth parameters, e.g., InAs amount and growth rate together with the pyramid top surface size. The QD number, related to the specific shape of the pyramid top surface, is reduced by the shrinking pyramid top surface size during growth. Well defined positioning of four, three, two, and single QDs is realized successfully. Regrowth of a passive InP structure around the pyramids establishes submicrometer-scale active-passive integration for efficient microcavity QD nanolasers and single photon sources operating in the 1.55-µm telecom wavelength region and their implementation in photonic integrated circuits. © 2010 Copyright SPIE - The International Society for Optical Engineering. U7 - Export Date: 2 August 2010 U7 - Source: Scopus U7 - Art. No.: 76100N

We review our recent advances in the lateral ordering, position, and number control of self-organized epitaxial semiconductor quantum dots based on self-organized anisotropic strain engineering, growth on patterned substrates, and selective area growth.

We report the impact of base size and shape on the evolution control of multifaceted InP (100) nanopyramids grown by selective area metal organic vapor phase epitaxy. The pyramid top surfaces are composed of a (100) center facet surrounded by high-index {103} and {115} facets. Their arrangement and (relative) size depend on the size and shape of the pyramid top area. For a certain shape, only the (100) facet remains below a critical size of the top area. The arrangement and (relative) size of the top facets in turn are governed by the {110} and {111} side facets whose area (ratio) depends on the pyramid base size and shape. This self-consistently determines the ratio of the (100) top facet area and the sum of the {110} and {111} side facet areas as well as the height of the pyramids.

Distribution control of InAs quantum dots (QDs) on truncated InP pyramids by selective area growth is reported. The top surface of the pyramids is composed of a (100) facet and high-index facets aside. The arrangement of the facets is governed by the shape of the pyramid base and top surface area. The QDs preferentially nucleate on the high-index facets determining position and distribution. The QD number is reduced with shrinking top surface size. Positioning of four, three, two, and single QDs is realized depending on the top surface's shape and size. Emission from single QDs is observed at 1.55 µm. © 2009 American Institute of Physics.

InAs quantum dots (QDs) are grown on InP (1 0 0) substrates by metalorganic vapor-phase epitaxy and the optical quality depending on the InP capping procedure is evaluated. The thickness of the low-temperature (Low-T) InP cap layer directly on the QDs is crucial for the QD photoluminescence (PL) peak wavelength and efficiency when followed by high-temperature capping. With increase of the Low-T cap layer thickness, the PL peak redshifts and the efficiency increases up to a thickness of 8 nm after which the PL peak wavelength stays constant and the efficiency strongly decreases. This behavior is attributed to the balance between stability of the QDs and defect diffusion toward the QDs.

We report strongly modified optical emission of InAs/InP quantum dots (QDs) coupled to the surface plasmon resonance (SPR) of In nanoparticles grown by metal-organic vapor phase epitaxy. With increasing In deposition time, the In nanoparticle size increases and the SPR redshifts significantly. When overlapping with the SPR, the excited state photoluminescence of the QDs is strongly enhanced due to QD-SPR coupling while the ground state photoluminescence is quenched due to non-radiative energy transfer. This is underpinned by the wavelength dependence of the spontaneous emission decay time which shows an opposite trend compared to that of bare QDs. (C) 2013 AIP Publishing LLC.

We report on the shape and polarization control of site-controlled multiple and single InAs quantum dots (QDs) on InP pyramids grown by selective-area metal-organic vapor phase epitaxy. With increasing growth temperature the QDs elongate causing strong linear polarization of the photoluminescence. With reduced pyramid base/pyramid top area/QD number, the degree of polarization decreases, attributed to the symmetric pyramid top, reaching zero for single QDs grown at lower temperature. This control of linear polarization is important for entangled photon sources operating in the 1.55 µm wavelength region.

Position and distribution control of 1.55-μm InAs quantum dots (QDs) on truncated InP pyramids grown by selective area Metal Organic Vapor Phase Epitaxy (MOVPE) is reported. The arrangement of the {103}, {115}, and (100) facets on the pyramid top surface is governed by the shape of the pyramid base and top surface area. This allows the precise position and distribution control of the QDs due to preferential nucleation on the {103} and {115} facets. With shrinking QD number upon reduced top surface area, sharp emission from single QDs is observed at 1.55 μm. Regrowth of a passive InP structure around the pyramids establishes submicrometer-scale active-passive integration for efficient microcavity QD nanolasers and single photon sources operating in the 1.55-μm telecom wavelength region and their implementation in photonic integrated circuits.

The first butt joint integrated extended cavity InAs/InP (100) quantum dot (QD) Fabry-Perot laser emitting around 1.55 mum is demonstrated. Continuous wave lasing at room temperature on the QD ground state transition is achieved. The threshold current is comparable to that of all-active QD lasers. The Butt joint reflectivity for straight waveguides is below -40 dB.